Probe and optical tomography system

ABSTRACT

An optical fiber is disposed in the direction of axis of the outer envelope inside a tubular outer envelope. Light emitted from the front end of the optical fiber is collected and projected on a body-to-be-scanned disposed externally of the outer envelope, and converged on the body-to-be-scanned. The outer envelope is filled with liquid so that the optical fiber is in the liquid.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an optical probe, and more particularly to anoptical probe having a tubular outer envelope and having a function ofemitting light from the peripheral surface thereof and an opticaltomography system where such an optical probe is employed.

2. Description of the Related Art

As a conventional method for obtaining tomographic images of measurementtargets, such as living tissue, a method that obtains opticaltomographic images by OCT (Optical Coherence Tomography) measurement hasbeen proposed (refer to Japanese Unexamined Patent Publication Nos.6(1994)-165784 and 2003-139688). The OCT measurement is a type of lightinterference measurement method that utilizes the fact that lightinterference is detected only when the optical path lengths of dividedlight beams, that is, a measurement light beam and a reference lightbeam, match within a range of coherence length of a light source. Thatis, in this method, a low coherent light beam emitted from a lightsource is divided into a measuring light beam and a reference lightbeam, the measuring light beam is irradiated onto a measurement target,and the measurement light beam reflected by the measurement target isled to a combining means. Whereas the reference light beam is led to thecombining means after its optical path length is adjusted so that itsoptical path length equalizes to that of the reflected light from anarbitrary position in the object. Then the measuring light and thereference light are combined by the combining means, and the intensitiesthereof are detected by the light detector.

In order to obtain a one-dimensional tomographic image, an interferencestrength waveform according to the reflectance distribution along thesame axis as the direction of travel of the measuring light by scanningthe optical path length of the measuring light according to themeasuring area. That is, a reflected light intensity distributionaccording to the structure in the direction of depth of the object to bemeasured can be obtained. Further, when the projecting position of themeasuring light applied to the object is one-dimensionally scanned in adirection perpendicular to the optical axis by the use of a deflectingmeans or a physical means, a two dimensional tomography representing areflected light intensity distribution can be obtained. Further, whenthe projecting position of the measuring light is two-dimensionallyscanned in directions perpendicular to the optical axis, a threedimensional tomography representing a reflected light intensitydistribution can be obtained.

In the above OCT system, a tomographic image is obtained by changing theoptical path length of the reference light, thereby changing themeasuring position (the depth of measurement) in the object. Thistechnique is generally referred to as “TD-OCT (time domain OCT)”. Morespecifically, in the optical path length adjusting mechanism for thereference light disclosed in Japanese Unexamined Patent Publication No.6(1994)-165784, an optical system which collects the reference lightemitted from the optical fiber on a mirror is provided and the opticalpath length is adjusted by moving only the mirror in the direction ofthe optical axis of the reference light. Further, in the optical pathlength changing mechanism for the reference light disclosed in JapaneseUnexamined Patent Publication No. 2003-139688, the reference lightemitted from the optical fiber is turned to parallel light by a lens,the reference light in the form of parallel light is collected andcaused to enter the optical fiber again by an optical path lengthadjusting lens, and the optical path length adjusting lens is moved backand forth in the direction of the beam axis of the reference light.

Whereas, as a system for rapidly obtaining a tomographic image withoutchanging the optical path length of the reference light, there has beenproposed an optical tomography system for obtaining an opticaltomographic image by measurement of SD-OCT (spectral domain OCT). In theSD-OCT system, a tomographic image which is one-dimensional in theoptical axis is formed without physically scanning the optical pathlength, by dividing broad band, low coherent light into measuring lightand reference light by the use of an interferometer as in theabove-described TD-OCT system, substantially equalizing the measuringlight and the reference light to cause them to interfere with eachother, decomposing the interference light into the optical frequencycomponents, measuring the intensity of the interference light by theoptical frequency components by an array type detector and carrying outa Fourier analysis on the obtained spectral interference waveforms by acomputer. As in above-described TD-OCT system, a two-dimensional or athree-dimensional tomographic image can be obtained by scanning theprojecting position of the measuring light in directions perpendicularto the optical axis.

As another system for rapidly obtaining a tomographic image withoutchanging the optical path length of the reference light, there has beenproposed an optical tomography system for obtaining an opticaltomographic image by measurement of SS-OCT (swept source OCT) (refer to“Motion artifacts in optical coherence tomography with frequency-domainranging”, S. H. Yun et al., OPTICS EXPRESS, Vol. 12, No. 13, pp.2977-2998, 2004.). The SS-OCT system employs a light frequency tunablelaser as a light source. The high coherence laser beam is divided intomeasuring light and reference light. The measuring light is projectedonto the object and the reflected light from the object is led to thecombining means. The reference light is led to the combining means afterit is made substantially equal to the measuring light in the opticalpath length to cause the measuring light and the reference light tointerfere with each other, and the measuring light and the referencelight are combined by the combining means. The intensity of the combinedlight is detected by an optical detector. The intensity of theinterference light is measured by the frequency component by sweepingthe frequency of the light frequency tunable laser and a one-dimensionaltomography in the optical axis is formed without physically scanning theoptical path length by Fourier-transforming the spectral interferencewaveform thus obtained with a computer. As in above-described TD-OCTsystem, a two-dimensional or a three-dimensional tomographic image canbe obtained by scanning the projecting position of the measuring lightin directions perpendicular to the optical axis.

There has been investigated application of the optical tomography systemof each of the systems described above to a measurement in an organicbody by a combination of an endoscope. In the optical tomography systemof each of the systems described above, a tomographic image along acertain surface of the object is generally obtained and it is necessaryto at least one-dimensionally scan the measuring light beam in theobject in perpendicular to the optical axis for this purpose. As a meansfor effecting such a light scanning, there has been known, as disclosedin Japanese Unexamined Patent Publication No. 4(1992)-135550, an opticalprobe having a tubular outer envelope and having a function ofdeflecting light emitted from the peripheral surface thereof in thedirection of circumference of the outer envelope. More specifically, theoptical probe comprises an inserting portion (outer envelope) which isinserted into the sample, a rotatable hollow shaft which is insertedinside the outer envelope, an optical fiber which is passed through theshaft, and a light deflecting element which is connected to the frontend portion of the shaft to be rotated together therewith and deflectslight radiated from the front end portion of the optical fiber in adirection of circumference of the outer envelope.

When an optical probe such as disclosed in Japanese Unexamined PatentPublication No. 4(1992)-135550 is inserted into an organic body, astress change or a temperature fluctuation due to a local pressurechange or a local bending of the optical fiber cannot be avoided. Therehas been well known the fact that when an outer pressure or a strain ora temperature change is imparted to a fiber in an interferometer whichmeasures the interference by the use of the fibers, the refractive indexof the fiber or the physical length of the fiber changes and the opticalpath length in the fiber changes up to 10 times the wavelength.Although, in the TD-OCT system, the difference hardly affects theresolution of the measured data since the difference is sufficientlysmall because the optical path length of reference light is scanned athigh speed to obtain a caustic line of the interference signal. However,in the SS-OCT system or the SD-OCT system described above, strain ordelete of information can be generated if the optical path lengthchanges during measurement since the interference waveform of light ismeasured in the wavelength of the range with the optical path length ofthe reference light fixed in the SS-OCT system or the SD-OCT system.

Specifically, in the SS-OCT system, since the optical path length of onelight shifts and the phase of the light shifts while the wavelength ofthe light source is scanned, the place shifted from the original placeis observed after Fourier transform is observed, which deteriorates theresolution. Further, in the SD-OCT system, where the signals areintegrally obtained, if the optical path length changes in a timeshorter than the time for which the shutter is opened, there gives riseto a problem that the signals are averaged and the S/N ratio of thesignal deteriorates.

SUMMARY OF THE INVENTION

In view of the foregoing observations and description, the primaryobject of the present invention is to provide an optical probe which cansuppress deterioration in measuring accuracy due to a stress change or atemperature fluctuation because of a local pressure change or a localbending.

Another object of the present invention is to provide an opticaltomography system which employs such an optical probe.

In accordance with the present invention, there is provided an opticalprobe comprising

a tubular outer envelope,

an optical fiber which is disposed in the direction of axis of the outerenvelope inside the outer envelope,

a light projecting means which collects light emitted from the front endof the optical fiber and projects it on a body-to-be-scanned disposedexternally of the outer envelope, and

a partition member which partitions the space between the outer envelopeand the optical fiber and between the outer envelope and the lightprojecting means into an optical-path-area including the optical path ofthe light emanating from the light projecting means, and anon-optical-path-area, a liquid layer being formed in thenon-optical-path-area.

Either liquid or gas may be filled in the optical-path-area. When liquidis filled in the optical-path-area, the liquid in the optical-path-areashould have a high transmittance to the wavelength of the light andshould be, for instance, water.

The partition member may be of any structure so long it partitions thespace into the optical-path-area and the non-optical-path-area. Forinstance, the partition member may closely enclose the optical fiber andthe liquid layer may be formed by filling liquid in the partitionmember.

An optical fiber holding portion for holding the optical member may beprovided between the outer envelope and the fiber. The optical fiber maycomprise only a core and a clad, or may comprise a coating member whichcoats the clad.

The optical probe may further comprise a pressure regulator whichregulates the pressure of the liquid to be substantially constant. Theoptical probe may further comprise a temperature regulator whichregulates the temperature of the liquid to be substantially constant.

In accordance with another aspect of the present invention, there isprovided an optical tomography system characterized in that an opticalprobe of the present invention is employed in each of the opticaltomography systems of the respective measurement systems describedabove. More specifically, the optical tomography system of the presentinvention comprises

a light source which emits light,

a light dividing means which divides light emitted from the light sourceinto measuring light and reference light,

a projecting optical system which projects the measuring light onto theobject,

a combining means which combines the reflected light from the objectwhen the measuring light is projected onto the object and the referencelight,

an interference light detecting means which detects interference lightof the reflected light and the reference light which have been combinedby the combining means, and

a tomographic image obtaining means which detects intensities of theinterference light in positions in the direction of depth of the objectand obtains a tomographic image of the object on the basis of theintensity of the reflected light in each position of the depth,

wherein the improvement comprises that the projecting optical systemincludes an optical probe in accordance with the present invention.

When gas or liquid having a high transmittance to the wavelength of thelight is filled in the optical-path-area, the liquid layer does notaffect the light led through the optical-path-area, whereby the materialof the liquid layer may have a larger heat capacity and may moresuppress the stress change.

When the partition member closely confines the optical fiber and theliquid layer is formed by filling liquid in the partition member, leakof liquid from the probe outer envelope can be surely prevented.

In accordance with an optical probe and an optical tomography systememploying the optical probe, since the optical probe comprises a tubularouter envelope, an optical fiber which is disposed in the direction ofaxis of the outer envelope inside the outer envelope, a light projectingmeans which collects light emitted from the front end of the opticalfiber and projects it on a body-to-be-scanned disposed externally of theouter envelope, and a partition member which partitions the spacebetween the outer envelope and the optical fiber and between the outerenvelope and the light projecting means into an optical-path-areaincluding the optical path of the light emanating from the lightprojecting means, and a non-optical-path-area and a liquid layer isformed in the non-optical-path-area, when the optical probe is insertedinto a living organization and a local pressure, stress change andtemperature change, due to bending are applied to the optical probe, theinfluence on the optical fiber in the probe outer envelope can besuppressed by the pressure in the partition member, and the measuringaccuracy can be prevented from deteriorating.

When an optical fiber holding portion for holding the optical member isprovided between the outer envelope and the fiber, the optical fiber isprevented from adhering to the inner surface of the probe outer envelopeand application of localized pressure to the optical fiber is avoided,whereby the measuring accuracy can be prevented from deteriorating.

Further, when a temperature regulator which regulates the temperature ofthe liquid to be substantially constant is further provided, change ofthe optical path length in the optical fiber can be prevented, wherebythe measuring accuracy can be prevented from deteriorating.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view partly cutaway showing an optical probe inaccordance with a first embodiment of the present invention,

FIG. 2 is a perspective view of an optical tomographic system to whichthe optical probe of FIG. 1 is applied,

FIG. 3 is a side view partly cutaway showing an optical probe inaccordance with a second embodiment of the present invention,

FIGS. 4A to 4C are side views partly cutaway showing an optical probesin accordance with a third embodiment of the present invention andmodification thereof,

FIG. 5 is a side view partly cutaway showing an optical probe inaccordance with a fourth embodiment of the present invention,

FIG. 6 is a side view partly cutaway showing an optical probe inaccordance with a fifth embodiment of the present invention,

FIG. 7 is a schematic view showing an example of the optical tomographysystem by the SD-OCT measurement to which the optical probe of thepresent invention is applied,

FIG. 8 is a schematic view showing an example of the optical tomographysystem by the SS-OCT measurement to which the optical probe of thepresent invention is applied, and

FIG. 9 is a schematic view showing an example of the optical tomographysystem by the TD-OCT measurement to which the optical probe of thepresent invention is applied.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will be described in detail withreference to the drawings, hereinbelow. FIG. 1 shows a side shape partlycut-away of an optical probe 10 in accordance with a first embodiment ofthe present invention. The optical fiber 10, for example, forms a frontend portion of an endoscope which forms a part of an optical tomographysystem. FIG. 2 shows an overall shape of the optical tomography system.

The optical tomography system will be first described in brief withreference to FIG. 2. The system comprises an endoscope 50 including theoptical probe 10; a light source unit 51, a video processor 52, and anoptical tomographic processing system 53 to which the endoscope 50 isconnected; and a monitor 54 connected to the video processor 52. Theendoscope 50 comprises an outer envelope 11 which is flexible andelongated, a control portion 56 connected to the rear end of theendoscope outer envelope 11 and a universal code 57 which extendsoutward from a side portion of the control portion 56.

A light guide (not shown) which transmits illuminating light from thelight source unit 51 is passed through the universal code 57, and alight source connector 58 which is removably connected to the lightsource unit 51 is provided on the end of the universal code 57. A signalcable 59 extends from the light source connector 58 and a signalconnector 60 which is removably connected to the video processor 52 isprovided on the end of the signal cable 59. The light source unit 51 isfor projecting the illuminating light onto a part of a sample 70 atomographic image of which is to be obtained as described later.

A bight control knob 61 for controlling a bight portion provided in theprobe outer envelope 11 and a light guide drive portion 62 are providedon the control portion 56, and the light guide drive portion 62 and theoptical tomographic processing system 53 are connected to each other byway of a light guide 63. The probe outer envelope 11 is inserted intothe sample 70 such as a human organ.

The optical probe 10 will be described with reference to FIGS. 1 and 2,hereinbelow. The optical probe 10 comprises: a cylindrical probe outerenvelope 11 having a closed front end; a single optical fiber 13, whichis provided inside the outer envelope 11 to extend in the direction ofthe axis of the outer envelope 11; and a gear 14 a fixed to a part ofthe outer peripheral surface of the optical fiber 13, a gear 14 b inmesh with the gear 14 a and a motor 15 which rotates the gear 14 b.

The optical probe 10 is further provided with a rod lens 18 fixed to thefront end of the optical fiber 13 and a prism mirror 17 fixed to the rodlens 18. The prism mirror 17 is rotated together with the optical 13 todeflect by 900 light L emitted from the front end of the optical fiber13 in the circumferential direction of the probe outer envelope 11, andthe rod lens 18 collects light L emitted from the front end of theoptical fiber 13 to converge on the sample 70 as the object to bescanned which is disposed externally of the circumference of the outerenvelope 11. In this particular embodiment, the rod lens 18 and theprism mirror 17 double as a light-guide means which leads the light Lreflected by the sample 70 to the front end of the optical fiber 13 toenter the optical fiber 13 from the front end as will be describedlater.

A partition member 19 which partitions the space formed between theprobe outer envelope 11 and the optical fiber 13 and between the probeouter envelope 11 and the projecting means (the prism mirror 17 and therod lens 18) into an optical path area R1 including the optical path ofthe light L emitted from the light projecting means and a non-opticalpath area R2. A partition member 16 is also provided in the base tableof the probe outer envelope 11, and a liquid layer 12 is formed in thenon-optical path area R2 closely enclosed by the partition members 16and 19. The liquid layer 12 comprises liquid of high viscosity like anoil in order to suppress the pressure to the optical fiber 13 andsmoothly rotate the same. On the other hand, a medium (e.g., air orwater) which is high in transmittance to the wavelength of light L to beemployed is filled in the optical path area R1.

An incident optical system 20 is disposed inside the endoscope 50 to beopposed to the base end of the optical fiber 13 as shown in FIG. 2.Light L propagating the light guide 63 and emitted from the light guide63 is collected by the incident optical system 20 and enters the opticalfiber 13 from the base end thereof.

Operation of the optical probe 10 will be described, hereinbelow. Alight source such as a laser (not shown) is disposed in the opticaltomographic processing system 53 shown FIG. 2, and the light L such as alaser beam emitted therefrom enters the light guide 63 and propagatestherethrough. The light L entering the optical fiber 13 (FIG. 1) by wayof the incident optical system 20 propagates through the optical fiber13, is emitted from the front end thereof, is reflected by 90° by theprism mirror 17 after collected by the rod lens 18 and is emittedoutside the probe 10 through the outer envelope 11 which islight-transmittable. Then when the motor 15 is driven, the optical fiber13 rotates as described above and the prism mirror 17 and the rod lens18 fixed thereto are rotated together with the optical fiber 13.

In response to rotation of the prism mirror 17, the light L emittedtherefrom is deflected in the circumferential direction of the probeouter envelope 11, thereby scanning the sample 70 in the direction ofarrow R in FIG. 2. The light L is reflected by the sample 70 whilescattering and a part of the reflected light impinges upon the prismmirror 17 and is reflected toward the rod lens 18. The part of thereflected light is collected by the rod lens 18 and enters the opticalfiber 13 from the front end thereof.

The reflected light thus propagating through the optical fiber 13 isemitted from the base end of the optical fiber 13, enters the lightguide 63 by way of the incident optical system 20 shown in FIG. 2, andpropagates through the light guide 63 to be transmitted to the opticaltomographic processing system 53. In the optical tomographic processingsystem 53, the above described reflected light is branched from theoptical path of the light L to the optical probe 10, and is detected byan optical detector (not shown). A tomographic image of the sample 70 isformed on the basis of the output of the optical detector and thetomographic image is displayed on the monitor 54.

At this time, when the liquid layer 12 is formed in the non-optical patharea R2, the force applied from the probe outer envelope 11 isdistributed to the whole under the Pascal's law in the liquid layer 12even if a stress change takes place due to a local pressure change orbending generated when the optical probe 10 is inserted into a livingorganism or after the optical probe 10 is inserted into a livingorganism. Accordingly, a local stress change applied to the opticalfiber 13 can be suppressed, and deterioration of, for instance,resolution by an optical path change due to a pressure change can bereduced.

Even if a temperature change, especially a temperature change which islocalized and sharp, takes place in response to insertion of the opticalprobe 10 into a living organism, the localized temperature change isdispersed by the heat capacity of the overall liquid layer 12 and theresponse time can be delayed. By this, the influence on the data strainof the OCT system can be reduced.

Second to fifth embodiments of the present invention will be describedwith reference to FIGS. 3 to 6, hereinbelow. In FIGS. 3 to 6, theelements analogous to those in FIGS. 1 and 2 are given the samereference numerals and will not be described unless necessary.

The second embodiment of the present invention will be first describedwith reference to FIG. 3. In the optical probe 100 of the secondembodiment, a partition member 112 is provided to closely enclose theoptical fiber 13, and the liquid layer 12 is formed by filling liquid inthe partition member 112. That is, a non-optical-path area R2 formed byfilling a liquid is formed between the partition member 112 and theoptical fiber 13 and a vacant space is formed between the partitionmember 112 and the optical fiber 13. The partition member 112 is rotatedtogether with the optical fiber 13. With this arrangement, the liquidcan be prevented from escaping outside in case that the probe outerenvelope 11 is damaged.

Although, in FIG. 3, the partition member 112 is provided on the opticalfiber 13 over substantially the entire range of the longitudinaldirection thereof, the partition member 112 closely enclosing liquid maybe provided in only the part where it has been empirically known thatthe bending stress is apt to be generated.

A third embodiment of the present invention will be described withreference to FIGS. 4A to 4C, hereinbelow. In the optical probe 120 ofthe third embodiment, a fiber holding member 121 is provided between theprobe outer envelope 11 and the optical fiber 13. The fiber holdingmember 121 extends from the inner surface of the probe outer envelope 11toward the center and fixes the optical fiber 13 to the vicinity of thecenter of the probe outer envelope 11. By thus providing the fiberholding member 121, the optical fiber 13 is prevented from adhering tothe inner surface of the probe outer envelope 11 and application oflocalized pressure to the optical fiber 13 is avoided, whereby themeasuring accuracy can be prevented from deteriorating. The fiberholding member 121 may be of soft material so that it also functions asa cushion member.

Although, in FIG. 4A, the fiber holding member 121 is in a directcontact with the optical fiber 13, the optical fiber 13 may be coatedwith a coating member 122 and the fiber holding member 121 may hold thecoating member 122 as shown in FIG. 4B. Further, instead of theabove-described coating member 122, the partition member 112 closelyenclosing a liquid may be employed as shown in FIG. 4C. With thisarrangement, one of the liquid or the coating member 122 functions as acushion member and the optical fiber can be prevented from being damagedeven if a localized pressure is generated.

A fourth embodiment of the present invention will be described withreference to FIG. 5, hereinbelow. In the optical probe 140 of the fourthembodiment, a pressure regulator 141 which holds constant the pressureof the liquid layer 12 in the probe outer envelope 11 is provided. Thepressure regulator 141 comprises, for instance, a spring connected tothe partition member 16, and holds constant the internal pressure of theliquid layer 12 by compressing the spring when a pressure is appliedfrom the external of the probe outer envelope 11, thereby dispersingconstant the pressure applied to the optical fiber 13. With thisarrangement, the stress change due to the localized pressure describedabove or the bending of the optical fiber can be absorbed by thepressure regulator 141, and the measuring accuracy can be prevented fromdeteriorating.

Although, in the illustrated embodiment, the pressure regulator 141comprises a spring, the pressure regulator 141 may be of any mechanismsuch as a hydraulic mechanism or a pneumatic mechanism so long as it isemployed to generally adjust a pressure. Further, by forming thepartition member from rubber-like material having an elasticity, thepartition member itself may be caused to function as a pressureregulator 141.

A fifth embodiment of the present invention will be described withreference to FIG. 6, hereinbelow. In the optical probe 160 of the fifthembodiment, a temperature regulator 161 which regulates the temperatureof the liquid in the liquid layer 12 to be substantially constant isprovided. The temperature regulator 161 regulates the temperature of theliquid in the liquid layer 12 to be substantially constant byheating/cooling the liquid layer or by circulating the liquid in theliquid layer 12 between an external reservoir (not shown). With thisarrangement, temperature fluctuation of the optical fiber 13 issuppressed and the optical path length change is prevented, wherebydeterioration of measurement accuracy can be prevented. Although, in theembodiment illustrated in FIG. 6, the probe outer envelope 11 is filledwith liquid, the temperature of the liquid filled in the partitionmember 112 may be similarly regulated to be substantially constant.

Examples of the optical tomography system to which the optical probes ofthe present invention are to be applied will be described, hereinbelow.The optical tomography system 1 shown in FIG. 7 is for obtaining atomographic image of an object of measurement such as a living tissue ora cell in a body cavity by measuring the SD-OCT. The optical tomographysystem 1 comprises: a light source unit 210 which emits light La; alight dividing means 3 which divides the light La emitted from the lightsource unit 210 into measuring light L1 and reference light L2; anoptical path length adjusting means 220 which adjusts the optical pathlength of the reference light L2 divided by the light dividing means 3;an optical probe 10 which guides to the object Sb to be measured themeasuring light beam L1 divided by the light dividing means 3; acombining means 4 for combining a reflected light beam L3 from theobject Sb when the measuring light beam L1 is irradiated onto the objectSb from the probe 10, and the reference light beam L2; and aninterference light detecting means 240 for detecting interference lightbeam L4 of the reflected light beam L3 and the reference light beam L2which have been combined by the combining means 4.

The light source unit 210 comprises a light source 111 which emits lowcoherence light La such as an SLD (super luminescent diode), ASE(amplified spontaneous emission) or a super continuum where an ultrashort pulse laser beam is projected onto a nonlinear medium to obtainbroad band light and an optical system 112 which enters the lightemitted from the light source 111 into an optical fiber FB1.

The light dividing means 3 comprises, for instance, a 2×2 fiber opticcoupler and divides the light beam La led thereto by way of the opticalfiber FB1 from the light source unit 210 into the measuring light beamL1 and the reference light beam L2. The light dividing means 3 isoptically connected to two optical fibers FB2 and FB3, and the measuringlight beam L1 is propagated through the optical fiber FB2 while thereference light beam L2 is propagated through the optical fiber FB3. Inthis embodiment, the light dividing means 3 also functions as thecombining means 4.

The optical probe 10 previously shown in FIG. 1 is optically connectedto the optical fiber FB2 and the measuring light beam L1 is guided tothe probe 10 from the optical fiber FB2. The probe 10 is inserted into abody cavity, for instance, through a forceps port by way of a forcepschannel and is removably mounted on the optical fiber FB2 by an opticalconnector 31.

The optical path length adjusting means 220 is disposed on the side ofthe optical fiber FB3 radiating the reference light beam L2. The opticalpath length adjusting means 220 changes the optical path length of thereference light beam L2 in order to adjust an initiating position of arange over which a tomographic image is to be obtained and comprises areflecting mirror 22 which reflects the reference light beam L2 radiatedfrom the optical fiber FB3, a first lens 21 a disposed between thereflecting mirror 22 and the optical fiber FB3, and a second lens 21 bdisposed between the first lens 21 a and the reflecting mirror 22.

The first lens 21 a makes parallel the reference light beam L2 radiatedfrom the core of the optical fiber FB3 and at the same time, collectsthe reference light beam L2 reflected by the reflecting mirror 2 on thecore of the optical fiber FB3. The second lens 21 b collects thereference light beam L2 made parallel by the first lens 21 a on thereflecting mirror 22 and at the same time, makes parallel the referencelight beam L2 reflected by the reflecting mirror 22. That is, the firstand second lenses 21 a and 21 b form a confocal optical system.

Accordingly, the reference light beam L2 radiated from the optical fiberFB3 is turned to a parallel light by the first lens 21 a and iscollected on the reflecting mirror 22 by the second lens 21 b.Subsequently, the reference light beam L2 reflected by the reflectingmirror 22 is turned to a parallel light by the second lens 21 b and iscollected on the core of the optical fiber FB3 by the first lens 21 a.

The optical path length adjusting means 220 is further provided with abase table 23 to which the second lens 21 b and the reflecting mirror 22are fixed and a mirror movement means 24 which moves the base table 23in the direction of the optical axis of the first lens 21 a. In responseto movement of the base table 23 in the direction of arrow A, theoptical path length of the reference light beam L2 can be changed.

The combining means 4 comprises a 2×2 fiber optic coupler as describedabove, and combines the reference light beam L2 which has been shiftedin its frequency and has been changed in its optical path length by theoptical path length adjusting means 220 and the reflected light beam L3from the object Sb to emit the combined light beam toward theinterference light detecting means 240 by way of an optical fiber FB4.

The interference light detecting means 240 detects interference light L4of the reflected light beam L3 and the reference light beam L2 whichhave been combined by the combining means 4, and comprises a collimatorlens 141 which makes parallel the interference light beam L4 radiatedfrom the optical fiber FB4, a spectral means 142 which divides theinterference light beam L4, having a plurality of wavelength bands, bythe wavelength bands and a light detecting means 144 which detects eachwavelength band of the interference light beam L4 divided by thespectral means 142.

The spectral means 142 comprises, for instance, a diffraction gratingelement, and spectrally divides the interference light beam L4 enteringit to output the divided interference light beam L4 to the lightdetecting means 144. The light detecting means 144 is formed by, forinstance, a CCD element which comprises a plurality of, for instance,one-dimensionally or two-dimensionally arranged photosensors and each ofthe photosensors detects each wavelength band of the interference lightbeam L4 spectrally divided as described above.

The light detecting means 144 is connected to an image obtaining means250 comprising, for instance, a computer system such as a personalcomputer. The image obtaining means 250 is connected to a display system260 formed, for instance, by a CRT or a liquid crystal display system.

Operation of the optical tomography system 1 having a structuredescribed above will be described, hereinbelow. When a tomographic imageis to be obtained, the optical path length is first adjusted by movingthe base 23 in the direction of the arrow A so that the object Sb ispositioned in the measurable area. The light beam La is emitted from thelight source unit 210 and the light beam La is divided into themeasuring light beam L1 and the reference light beam L2 by the lightdividing means 3. The measuring light beam L1 is radiated from theoptical probe 10 toward a body cavity and is projected onto the objectSb. At this time, the measuring light beam L1 radiated from the opticalprobe 10 is caused to one-dimensionally scan the object Sb by theoptical probe 10 operating as described above. Then the reflected lightbeam L3 from the object Sb and the reference light beam L2 reflected bythe reflecting mirror 22 are combined, and the interference light beamL4 of the reflected light beam L3 and the reference light beam L2 isdetected by the interference light detecting means 240. Information onthe intensity distribution of the reflected light in the direction ofdepth of the object Sb is obtained by carrying out Fourier transform onthe detected interference light beam L4 in the image obtaining means 250after carrying out a suitable waveform compensation and noise removal.

By causing the measuring light beam L1 to scan the object Sb by theoptical probe 10 as described above, information on the direction ofdepth of the object Sb along the direction of scan is obtained andaccordingly tomographic images on the cross-section including thedirection of scan can be obtained. The tomographic images thus obtainedare displayed by the display system 260. Further, for instance, bymoving the optical probe 10 right and left in FIG. 7 so that themeasuring light L1 scans the object Sb in a second directionperpendicular to said direction of scan, tomographic images on thecross-section including the second direction can be further obtained.

Another example of the optical tomography system to which the opticalprobes of the present invention are to be applied will be described,hereinbelow. The optical tomography system 300 shown in FIG. 8 is forobtaining a tomographic image of the object of measurement by measuringthe SS-OCT and specifically differs from the optical tomography system 1shown in FIG. 7 in structure of the light source unit and theinterference light detecting means.

The light source unit 310 of this system emits a laser beam La whilesweeping its wavelength at a predetermined period. Specifically, thelight source unit 310 comprises a semiconductor optical amplifier (asemiconductor gain medium) 311 and an optical fiber FB10 connected tothe semiconductor optical amplifier 311 at opposite ends thereof. Thesemiconductor optical amplifier 311 emits weak light to one end of theoptical fiber FB10 in response to injection of a drive current andamplifies light input from the other end of the optical fiber FB10. Whena drive current is supplied to the semiconductor optical amplifier 311,a pulse-like laser beam La is emitted to the optical fiber FB1 by aresonator formed by the semiconductor optical amplifier 311 and theoptical fiber FB10.

Further, an optical divider 312 is connected to the optical fiber FB10and a part of the light beam propagated through the optical fiber FB10is emitted from the optical divider 312 toward the optical fiber FB11.Light emitted from the optical fiber FB11 travels through the collimatorlens 313, the diffraction grating element 314 and the optical system 315and is reflected by the rotating polygon mirror 316. The reflected lightis returned to the optical fiber FB11 by way of the optical system 315,the diffraction grating element 314 and the collimator lens 313.

The rotating polygon mirror 316 rotates in the direction indicated byarrow R1, to vary the angle of each reflective surface thereof withrespect to the optical axis of the optical system 315. Thereby, only alight beam having a specific frequency, among the light spectrally splitby the diffraction grating 314, is returned to the optical fiber FB11.The frequency of the light beam that reenters the optical fiber FB1 isdetermined by the angle formed by the optical axis of the optical system315 and the reflective surface of the rotating polygon mirror 316. Thenthe light beam of a specific frequency band impinging upon the opticalfiber FB11 enters the optical fiber FB10, and as a result, only a laserbeam La of the specific frequency band is emitted toward the opticalfiber FB1.

Accordingly, when the rotating polygon mirror 316 rotates in thedirection indicated by arrow R1 at a constant speed, the wavelength λ ofthe light beam which reenters the optical fiber FB11 changes at a periodwith time. As a result, a laser beam La which is swept in its wavelengthis emitted from the light source unit 310 toward the optical fiber FB1.

The interference light detecting means 240 detects interference lightbeam L4 of the reflected light beam L3 and the reference light beam L2which have been combined by the combining means 4 and the imageobtaining means 250 detects the intensities of the reflected light beamL3 in positions in the direction of depth of the object Sb by carryingout Fourier transform on the interference light beam L4 detected by theinterference light detecting means 240 and obtains a tomographic imageof the object Sb. The tomographic images thus obtained are displayed bythe display system 260. In this embodiment, a mechanism where theinterference light L4 is divided into a pair of lights by the fibercoupler which are guided to optical detectors 40 a and 40 b and abalanced detection is carried out in a calculating means 241 is formed.As can be understood, in this embodiment, the interference lightdetecting means 240 is formed by the optical detectors 40 a and 40 b andthe calculating means 241.

Here, detection of the interference light beam L4 in the interferencelight detecting means 240 and image generation in the image obtainingmeans 250 will be described briefly. Note that a detailed description ofthese two points can be found in “Optical Frequency ScanningInterference Microscopes”, M. Takeda, Optics Engineering Contact, Vol.41, No. 7, pp. 426-432, 2003.

When the measuring light beam L1 is projected onto the object Sb, thereflected light L3 from each depth of the object Sb and the referencelight L2 interfere with each other with various optical path lengthdifference l. When the light intensity of the interference fringe atthis time versus each optical path length difference is assumed to beS(l), the light intensity I(k) detected in the interference lightdetecting means 240 is expressed by the following formula.

I(k)=∫₀ ^(∞) S(l)[l+cos (kl)]dl

wherein k represents the wave number and l represents the optical pathlength difference. The above formula may be considered to be given as aninterferogram of a light frequency range having a wave number of ω/c(k=ω/c) as a variable. Accordingly, a tomographic image is generated byobtaining in the image obtaining means 250 information on the distanceof the object Sb from the measurement initiating position andinformation on the intensity of reflection by carrying outFourier-transform on the spectral interference fringes detected by theinterference light detecting means 240 and determining the intensityS(l) of the interference light beam L4.

In the optical tomography system 300, an optical probe 10 the same inarrangement as that employed in the system of FIG. 7 is employed and theoperation is the same as that employed in the system of FIG. 7.

Still another example of the optical tomography system to which theoptical probes of the present invention are to be applied will bedescribed, hereinbelow. The optical tomography system 400 shown in FIG.9 is for obtaining a tomographic image of the object of measurement bymeasuring the TD-OCT and comprises a light source unit 210 provided witha light source 111 which emits laser light La and a light collectinglens 112, a light dividing means 2 which divides a laser light Laemitted from the light source unit 210 and propagated through theoptical fiber FB1, a light dividing means 3 which divides the laserlight La passing therethrough into measuring light L1 and referencelight L2, an optical path length adjusting means 220 which adjusts theoptical path length of the reference light L2 divided by the lightdividing means 3 and propagated through the optical fiber FB3, anoptical probe 10 which projects onto the object Sb the measuring lightL1 divided by the light dividing means 3 and propagated through theoptical fiber FB2, a combining means 4 (the light dividing means 3doubles) which combines the reflected light L3 from the object Sb whenthe measuring light L1 divided by the light dividing means is projectedonto the object Sb and the reference light L2, and an interference lightdetecting means 240 which detects interference light L4 of the reflectedlight L3 and the reference light L2 which have been combined by thecombining means 4.

The optical path length adjusting means 220 comprises a collimator lens21 which makes parallel the reference light beam L2 radiated from theoptical fiber FB3, a reflecting mirror 23 which is movable in thedirection of arrow A to change the distance from the collimator lens 21,and a mirror moving means 24 which moves the reflecting mirror 23 andchanges the optical path length of the reference light L2 in order tochange the measuring position in the object Sb in the direction ofdepth. The reference light L2 which has been changed in its optical pathlength by the optical path length adjusting means 220 is guided to thecombining means 4.

The interference light detecting means 240 detects the intensity of theinterference light L4 propagating through the optical fiber FB2 from thecombining means 4. Specifically, only when the optical length differencebetween the sum of the total optical path length of the measuring lightL1 and the optical path length of the reflected light L3 reflected orscattered rearward at a certain point on the object Sb and the referencelight L2 is smaller than the coherence length of the light source, aninterference signal whose amplitude is proportional to the amount of thereflected light is detected. Further, as the optical path length isscanned by the optical path length adjusting means 220, the position ofthe reflecting point (depth) in which the interference signal isobtained is changed, whereby the interference light detecting means 240detects a reflectance signal in each measuring position of object Sb.Information on the measuring position is output from the optical pathlength adjusting means 220 to the image obtaining means. On the basis ofthe signals detected by the interference light detecting means 240 andinformation on the measuring position in the mirror moving means 24,information on the intensity distribution of the reflected light in thedirection of depth of the object Sb is obtained by the image obtainingmeans 250.

By causing the measuring light beam L1 to scan the object Sb by theoptical probe 10 as described above, information on the direction ofdepth of the object Sb is obtained and accordingly tomographic images onthe cross-section including the direction of scan can be obtained. Thetomographic images thus obtained are displayed by the display system260. Further, for instance, by moving the optical probe 10 right andleft in FIG. 7 so that the measuring light L1 scans the object Sb in asecond direction perpendicular to said direction of scan, tomographicimages on the cross-section including the second direction can beobtained.

In the optical tomography system 400, an optical probe 10 the same inarrangement as that employed in the system of FIG. 7 is also employedand the operation is the same as that employed in the system of FIG. 7.

Although the optical tomography systems 1, 300 and 400 in which theoptical probe 10 is employed, the optical probes 100, 120, 140 and 160in accordance with previously described other embodiments of the presentinvention may be, of course, employed instead of the optical probe 10.

1. An optical probe comprising a tubular outer envelope, an opticalfiber which is disposed in the direction of axis of the outer envelopeinside the outer envelope, a light projecting means which collects lightemitted from the front end of the optical fiber and projects it on abody-to-be-scanned disposed externally of the outer envelope, and apartition member which partitions the space between the outer envelopeand the optical fiber and between the outer envelope and the lightprojecting means into an optical-path-area including the optical path ofthe light emanating from the light projecting means, and anon-optical-path-area, a liquid layer being formed in thenon-optical-path-area.
 2. An optical probe as defined in claim 1 inwhich gas is filled in the optical-path-area.
 3. An optical probe asdefined in claim 1 in which a liquid having a high transmittance to thewavelength of the light is filled in the optical-path-area.
 4. Anoptical probe as defined in claim 1 in which the partition memberclosely encloses the optical fiber and the liquid layer is formed byfilling liquid in the partition member.
 5. An optical probe as definedin claim 1 in which an optical fiber holding portion for holding theoptical member is provided between the outer envelope and the fiber. 6.An optical probe as defined in claim 1 in which the optical fiber iscoated with a coating member.
 7. An optical probe as defined in claim 1further comprising a pressure regulator which regulates the pressure ofthe liquid to be substantially constant.
 8. An optical probe as definedin claim 1 further comprising a temperature regulator which regulatesthe temperature of the liquid to be substantially constant.
 9. Anoptical tomography system comprising a light source which emits light, alight dividing means which divides light emitted from the light sourceinto measuring light and reference light, a projecting optical systemwhich projects the measuring light onto the object, a combining meanswhich combines the reflected light from the object when the measuringlight is projected onto the object and the reference light, aninterference light detecting means which detects interference light ofthe reflected light and the reference light which have been combined bythe combining means, and a tomographic image obtaining means whichdetects intensities of the interference light in positions in thedirection of depth of the object and obtains a tomographic image of theobject on the basis of the intensity of the reflected light in eachposition of the depth, wherein the improvement comprises that theprojecting optical system includes an optical probe as defined in claim1.